U.S. patent number 7,625,301 [Application Number 12/119,190] was granted by the patent office on 2009-12-01 for golf ball.
This patent grant is currently assigned to Bridgestone Sports Co., Ltd.. Invention is credited to Atsushi Komatsu.
United States Patent |
7,625,301 |
Komatsu |
December 1, 2009 |
Golf ball
Abstract
The invention provides a golf ball composed of a core, an
intermediate layer which encases the core, and a cover which
encases the intermediate layer. The core has a diameter of 36 to 40
mm and a deflection of 3.5 to 4.2 mm, and the intermediate layer
has a Shore D hardness of 45 to 55 and a thickness of 0.6 to 1.6
mm. The cover has a Shore D hardness of 63 to 66 and a thickness of
0.6 to 1.6. The ball as a whole has a deflection of 2.6 to 3.5 mm,
and the intermediate layer and cover have a combined thickness of
1.8 to 2.8 mm. The ball has a hardness design such that the Shore D
hardnesses of the ball components satisfy the relationship core
center.ltoreq.core surface.ltoreq.intermediate layer.ltoreq.cover,
and the cover is made of a material composed primarily of a
thermoplastic resin or a thermoplastic elastomer. The intermediate
layer is made of a material that is a resin composition in which at
least 90 mol % of the acid groups are neutralized. This combination
of characteristics provides the golf ball with a sufficient spin
rate-lowering effect, thus increasing the distance traveled, and
also confers the ball with a good feel on impact and an excellent
durability to cracking.
Inventors: |
Komatsu; Atsushi (Chichibu,
JP) |
Assignee: |
Bridgestone Sports Co., Ltd.
(Tokyo, JP)
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Family
ID: |
39742207 |
Appl.
No.: |
12/119,190 |
Filed: |
May 12, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080220900 A1 |
Sep 11, 2008 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11712964 |
Mar 2, 2007 |
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Current U.S.
Class: |
473/374 |
Current CPC
Class: |
A63B
37/0003 (20130101); A63B 37/06 (20130101); A63B
2209/00 (20130101); A63B 37/0017 (20130101); A63B
37/0018 (20130101); A63B 37/0021 (20130101); A63B
37/0031 (20130101); A63B 37/0033 (20130101); A63B
37/0034 (20130101); A63B 37/0043 (20130101); A63B
37/0045 (20130101); A63B 37/0048 (20130101); A63B
37/0062 (20130101); A63B 37/0064 (20130101); A63B
37/0065 (20130101); A63B 37/0075 (20130101); A63B
37/0004 (20130101) |
Current International
Class: |
A63B
37/06 (20060101) |
Field of
Search: |
;473/374,373,376,377 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2002-345999 |
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Dec 2002 |
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JP |
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2003-175130 |
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Jun 2003 |
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JP |
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3729243 |
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Oct 2005 |
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JP |
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3772252 |
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Feb 2006 |
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JP |
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2006-087948 |
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Apr 2006 |
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JP |
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98/46671 |
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Oct 1998 |
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WO |
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Primary Examiner: Trimiew; Raeann
Attorney, Agent or Firm: Sughrue Mion, PLLC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of application Ser. No.
11/712,964 filed on Mar. 2, 2007, the entire contents of which are
hereby incorporated by reference.
Claims
The invention claimed is:
1. A golf ball comprising a core, an intermediate layer which
encases the core, and a cover which encases the intermediate layer,
wherein the core has a diameter of between 36 and 40 mm and a
deflection of between 3.5 and 4.2 mm, the intermediate layer has a
Shore D hardness of between 45 and 55 and a thickness of between
0.6 and 1.6 mm, the cover has a Shore D hardness of between 63 and
66 and a thickness of between 0.6 and 1.6, the ball as a whole has
a deflection of between 2.6 and 3.5 mm, the intermediate layer and
cover have a combined thickness of between 1.8 and 2.8 mm, the ball
has a hardness design such that the Shore D hardnesses of the ball
components satisfy the relationship core center.ltoreq.core
surface.ltoreq.intermediate layer.ltoreq.cover, the cover is made
of a material composed primarily of a thermoplastic resin or a
thermoplastic elastomer, and the intermediate layer is made of a
material that is a resin composition containing a heated mixture
which has a melt flow rate according to JIS K-7210 of 0.5 to 1.0
g/l 0 mm and which is selected from among (I) to (III) below: (I)
(a) 100 parts by weight of an olefin-unsaturated carboxylic acid
random copolymer and/or an olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester random copolymer, (b) from 5
to 80 parts by weight of a fatty acid or fatty acid derivative
having a molecular weight of at least 280, and (c) from 0.1 to 20
parts by weight of a basic inorganic metal compound capable of
neutralizing the acid groups in components (a) and (b); (II) (d)
100 parts by weight of a metal ion neutralization product of an
olefin-unsaturated carboxylic acid random copolymer and/or a metal
ion neutralization product of an olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester random copolymer, (b) from 5
to 80 parts by weight of a fatty acid or fatty acid derivative
having a molecular weight of at least 280, and (c) from 0.1 to 20
parts by weight of a basic inorganic metal compound capable of
neutralizing the acid groups in components (d) and (b); (III) 100
parts by weight of, in admixture, (a) an olefin-unsaturated
carboxylic acid random copolymer and/or an olefin-unsaturated
carboxylic acid-unsaturated carboxylic acid ester random copolymer
and (d) a metal ion neutralization product of an olefin-unsaturated
carboxylic acid random copolymer and/or a metal ion neutralization
product of an olefin-unsaturated carboxylic acid-unsaturated
carboxylic acid ester random copolymer, (b) from 5 to 80 parts by
weight of a fatty acid and/or fatty acid derivative having a
molecular weight of at least 280, and (c) from 0.1 to 20 parts by
weight of a basic inorganic metal compound capable of neutralizing
the acid groups in components (a), (d) and (b); at least 90% of the
acid groups in the resin composition being neutralized, wherein the
cover material and the intermediate layer material have a melt flow
rate difference therebetween of at least 1.0 g/l 0 mm.
2. The golf ball of claim 1, wherein 100 mol % of the acid groups
in the resin composition serving as the intermediate layer material
are neutralized.
3. The golf ball of claim 1, wherein the core has a difference in
Shore D hardness between the core surface and the core center of
from 5 to 15.
4. The golf ball of claim 1 which has a surface on which a
plurality of dimples are formed, the dimples numbering in all from
250 to 370, having an overall volume of from 400 to 700 mm.sup.3,
and having a surface coverage of at least 79%.
5. The golf ball of claim 1, wherein the center of the core has a
Shore D hardness of 15 to 28 and the surface of the core has a
Shore D hardness of 30 to 50.
6. The golf ball of claim 1, wherein pentachlorothiophenol is not
included in the core.
7. The golf ball of claim 1 which has a surface on which a
plurality of dimples are formed, the dimples numbering in all from
270 to 350.
8. The golf ball of claim 1 which has a surface on which a
plurality of dimples are formed, the dimples having an overall
volume of from 450 to 650 mm.sup.3.
9. The golf ball of claim 1 which has a surface on which a
plurality of dimples are formed, the dimples numbering in all from
270 to 350 and having an overall volume of from 450 to 650
mm.sup.3.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a golf ball of three or more
layers, including a core, an intermediate layer and a cover, which
ball has an excellent feel on impact, controllability and flight
performance.
Golf club performance has been improving in recent years, one
effect of which has been a significant decline in the spin rate of
the golf ball after it is hit. However, the spin rate tends to
remain high under the hitting conditions of the average golfer
(golfers having an average score), which accounts for the majority
golfers. Hence, by achieving a lower ball spin rate, there remains
room for increasing the distance traveled by the ball.
Art for increasing the distance includes improvements to the
material making up the intermediate layer sandwiched between the
core and the cover serving as the outermost layer. For example,
JP-A 2003-175130 discloses a highly neutralized intermediate layer
material in which the degree to which an ionomer resin or the like
has been neutralized is set relatively high.
However, in such a golf ball, the use of a soft cover is presumed.
That is, the ball does not have a construction in which a hard
cover is used to take full advantage of the properties of a
high-resilience intermediate layer.
JP-A 2006-87948 teaches a golf ball which uses an intermediate
layer material having a high degree of neutralization. Such a ball
does have an improved rebound, but there remains room for
improvement as a spin rate-lowering construction.
Highly neutralized intermediate layer materials have also been
disclosed in, for example, JP No. 3729243, JP No. 3772252 and JP-A
2002-345999. However, in all of these disclosures, there remains
room for further improvement in terms of fully exploiting the high
resilience of the intermediate layer and reducing the spin rate.
Moreover, these prior-art golf balls leave something to be desired
not only in their distance of travel, but also in their feel on
impact and their durability to cracking.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
golf ball of three or more layers, including a core, an
intermediate layer and a cover, which ball, even when hit under
conditions typical of an average golfer using a driver, achieves a
sufficient reduction in the spin rate of the ball and thus
increases the distance of travel, and moreover has an excellent
feel on impact and an excellent durability to cracking.
Based on extensive investigations conducted in order to achieve the
above object, the inventor has found that if an intermediate layer
composed of a specific resin mixture and having a high resilience
is used, if the thicknesses and hardnesses of the intermediate
layer and a hard cover are selected so as to provide the
intermediate layer and the cover at optimal gages, if the diameter
and the deflection hardness of the core are optimized, and if the
ball is given a hardness design in which the Shore D hardnesses of
the respective parts of the ball satisfy the relationship core
center.ltoreq.core surface.ltoreq.intermediate layer.ltoreq.cover,
when the ball is played with a driver by an average golfer, a
sufficient spin rate-lowering effect will be achieved, increasing
the distance traveled by the ball. Moreover, the ball also will
have an excellent feel on impact and an excellent durability to
cracking.
That is, when a golf ball is hit with a driver, first a force acts
in such a way as to apply spin to the golf ball, then an opposite
force acts to suppress the spin. In the present invention, by
giving the intermediate layer a high resilience, the timing of the
switch to the force that acts to suppress spin is speeded up. As a
result, a lower spin rate is achieved. However, when the ball is
hit with a driver, if the rigidity of the cover is not maintained,
the intermediate layer will be flattened to such a degree that its
high resilience will be of no avail and a lower spin rate will not
be achieved. In view of this, the inventor has discovered that, to
maximize the force that suppresses spin, creating a ball
construction that combines a highly resilient intermediate layer
with a hard cover is very effective for achieving the objects of
the invention.
More specifically, the golf ball of the invention has a
construction that is able to achieve the maximum reduction in spin
rate, even among distance balls in which the distance traveled by
the ball when hit with a driver is of particular importance. In
prior-art distance balls, the two fundamental approaches have been:
(i) to make the cover hard so as to increase the initial velocity
of the ball on impact and thus achieve a reduced spin rate; and
(ii) to make the intermediate layer hard so as to increase the
initial velocity of the ball on impact and thus achieve a reduced
spin rate. A drawback of both such prior-art balls is the harder
feel on impact. Hence, to increase the distance traveled by the
ball while imparting a good feel on impact, the hardnesses of the
intermediate layer and the cover have been subject to certain
limits. The inventor thus conceived of a golf ball in which the
hardnesses of the cover and the intermediate layer are increased to
the upper limit at which the feel of the ball is not compromised,
and in which, by having the intermediate layer made of a
high-resilience material, the timing of the force that suppresses
ball spin is speeded up, enabling a reduced spin rate to be
achieved.
Accordingly, the invention provides the following golf balls. [1] A
golf ball comprising a core, an intermediate layer which encases
the core, and a cover which encases the intermediate layer, wherein
the core has a diameter of between 36 and 40 mm and a deflection of
between 3.5 and 4.2 mm, the intermediate layer has a Shore D
hardness of between 45 and 55 and a thickness of between 0.6 and
1.6 mm, the cover has a Shore D hardness of between 63 and 66 and a
thickness of between 0.6 and 1.6, the ball as a whole has a
deflection of between 2.6 and 3.5 mm, the intermediate layer and
cover have a combined thickness of between 1.8 and 2.8 mm, the ball
has a hardness design such that the Shore D hardnesses of the ball
components satisfy the relationship core center.ltoreq.core
surface.ltoreq.intermediate layer.ltoreq.cover, the cover is made
of a material composed primarily of a thermoplastic resin or a
thermoplastic elastomer, and the intermediate layer is made of a
material that is a resin composition containing a heated mixture
which has a melt flow rate according to JIS K-7210 of at least 0.5
g/10 min and which is selected from among (I) to (III) below: (I)
(a) 100 parts by weight of an olefin-unsaturated carboxylic acid
random copolymer and/or an olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester random copolymer, (b) from 5
to 80 parts by weight of a fatty acid or fatty acid derivative
having a molecular weight of at least 280, and (c) from 0.1 to 20
parts by weight of a basic inorganic metal compound capable of
neutralizing the acid groups in components (a) and (b); (II) (d)
100 parts by weight of a metal ion neutralization product of an
olefin-unsaturated carboxylic acid random copolymer and/or a metal
ion neutralization product of an olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester random copolymer, (b) from 5
to 80 parts by weight of a fatty acid or fatty acid derivative
having a molecular weight of at least 280, and (c) from 0.1 to 20
parts by weight of a basic inorganic metal compound capable of
neutralizing the acid groups in components (d) and (b); (III) 100
parts by weight of, in admixture, (a) an olefin-unsaturated
carboxylic acid random copolymer and/or an olefin-unsaturated
carboxylic acid-unsaturated carboxylic acid ester random copolymer
and (d) a metal ion neutralization product of an olefin-unsaturated
carboxylic acid random copolymer and/or a metal ion neutralization
product of an olefin-unsaturated carboxylic acid-unsaturated
carboxylic acid ester random copolymer, (b) from 5 to 80 parts by
weight of a fatty acid and/or fatty acid derivative having a
molecular weight of at least 280, and (c) from 0.1 to 20 parts by
weight of a basic inorganic metal compound capable of neutralizing
the acid groups in components (a), (d) and (b); at least 90% of the
acid groups in the resin composition being neutralized. [2] The
golf ball of [1], wherein 100 mol % of the acid groups in the resin
composition serving as the intermediate layer material are
neutralized. [3] The golf ball of [1], wherein the core has a
difference in Shore D hardness between the core surface and the
core center of from 5 to 15. [4] The golf ball of [1] which has a
surface on which a plurality of dimples are formed, the dimples
numbering in all from 250 to 370, having an overall volume of from
400 to 700 mm.sup.3, and having a surface coverage of at least 79%.
[5] The golf ball of [1], wherein the intermediate layer material
has a melt flow rate of from 0.5 to 1.0 g/10 min, and the cover
material and the intermediate layer material have a melt flow rate
difference therebetween of at least 1.0 g/10 min.
BRIEF DESCRIPTION OF THE DIAGRAMS
FIG. 1 is a schematic sectional view of a golf ball (3-layer
construction) according to an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The invention is described more fully below in conjunction with the
accompanying diagram. Referring to the diagram, the golf ball of
the invention has a construction of at least three layers which
includes a core 1, an intermediate layer 2 that encloses the core
1, and a cover 3 that encloses the intermediate layer 2. A
plurality of dimples D are formed on the surface of the cover 3. In
the arrangement shown in FIG. 1, the core 1, the intermediate layer
2 and the cover 3 are each composed of one layer, although any of
these components of the ball may be composed of a plurality of two
or more layers. If necessary, the core 1, the intermediate layer 2
and the cover 3 may each be composed of a plurality of layers. In
arrangements where the core, the intermediate layer and/or the
cover described below has a multilayer construction, all the
necessary conditions for a particular component shall be satisfied
for the plurality of layers making up that particular component as
a whole.
A known core material, such as a rubber composition, may be used in
the core of the inventive ball. The use of polybutadiene as the
base rubber is especially preferred. The polybutadiene is
exemplified by cis-1,4-polybutadiene having a cis structure of at
least 40%.
The rubber composition may include, as a crosslinking agent, a zinc
or magnesium salt of an unsaturated fatty acid, such as zinc
methacrylate or zinc acrylate, or an ester compound such as
trimethylpropane methacrylate. The use of zinc acrylate is
especially preferable for achieving a high resilience. Such a
crosslinking agent may be included in an amount of at least 5 parts
by weight but not more than 40 parts by weight per 100 parts by
weight of the base rubber.
The rubber composition may include also a vulcanizing agent, such
as dicumyl peroxide or a mixture of dicumyl peroxide and
1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclo-hexane. The amount of
vulcanizing agent included may be set to at least 0.1 part by
weight but not more than 5 parts by weight per 100 parts by weight
of the base rubber. A commercial product, such as Percumyl D
(produced by NOF Corporation) may be suitably used as the dicumyl
peroxide.
In addition, it is possible to include also an antioxidant and a
filler for regulating the specific gravity, such as zinc oxide or
barium sulfate. Such a filler may be incorporated in an amount of
from 0 part by weight to 130 parts by weight per 100 parts by
weight of the base rubber.
Also, in the present invention, it is preferable not to compound an
organosulfur compound such as pentachlorothiophenol into the core
material in order to prevent a spin rate-lowering effect of the
intermediate layer material having a high resilience when the
rebound of the core is enhanced. It may be conducted that the
adjustment of the initial velocity of the ball according to the
seasonal variation, and in light of considering of the above-point,
it is preferable to add the organosulfur in an amount of not more
than 0.1 part by weight per 100 parts by weight of the base
rubber.
To obtain a core from the above core-forming rubber composition,
the composition may be masticated with a conventional apparatus
such as a Banbury mixer, kneader or roll mill, and the resulting
compound compression-molded using a core mold.
In the practice of the invention, the center of the core must have
a Shore D hardness which satisfies the following relationships with
respect to the Shore D hardnesses of the subsequently described
intermediate layer and cover: hardness at center of
core.ltoreq.hardness of intermediate layer.ltoreq.hardness of
cover; preferably, hardness at center of core.ltoreq.hardness at
core surface.ltoreq.hardness of intermediate layer.ltoreq.hardness
of cover; and more preferably, the hardness increases gradually
from the center of the core to the outside surface of the cover.
These relationships are described more fully later in the
specification.
The Shore D hardness of the core is suitably adjusted in accordance
with the Shore D hardnesses of the intermediate layer and the cover
and is not subject to any particular limitation, provided it
satisfies the above relationship. However, it is advantageous for
the Shore D hardness at the center of the core to be generally not
more than 35, and preferably not more than 30, but at least 15, and
preferably at least 20. It is recommended that the Shore D hardness
at the surface of the core be suitably adjusted in accordance with
the Shore D hardness at the center of the core. A value of
generally not more than 50, and especially not more than 45, but at
least 30, and especially at least 35, is preferred.
The Shore D hardness difference between the core center and the
core surface, while not subject to any particular limitation, is
preferably at least 5 but not more than 15. This is because, while
it is generally thought that a larger core hardness gradient will
produce a better spin rate-lowering effect, in the present
invention, owing to the presence of a relatively hard cover, a
large core hardness gradient will result in a construction that
works against a spin rate-lowering effect, thus having instead an
adverse influence. Accordingly, when the cover is hard as in the
present invention, a smaller core hardness gradient will result in
a lower spin rate. That is, a modest core hardness gradient, such
as one which falls within the above range, is suitable for the core
structure of the invention.
The core in the invention has a diameter of at least 36 mm, and
preferably at least 37 mm, but not more than 40 mm, and preferably
not more than 39 mm. If the core diameter is too small, the
intermediate layer and the cover will be thicker, the feel of the
ball on impact will worsen, the spin rate will increase, and the
distance traveled by the ball will decrease. On the other hand, if
the core diameter is too large, the intermediate layer and the
cover will be thinner, and the durability to cracking and the scuff
resistance will worsen.
The core of the invention has a deflection (mm), when subjected to
a compressive load of 130 kgf from an initial load state of 10 kgf,
of preferably at least 3.5 mm, but preferably not more than 4.2 mm.
If the deflection by the core is smaller than that indicated above,
the feel on impact will be harder, which is not desirable. On the
other hand, if the deflection by the core is larger than that
indicated above, the ball as a whole will incur excessive
deformation, resulting in a decrease in the desirable effects of
the intermediate layer.
As shown in FIG. 1, in the golf ball of the invention, the core 1
has formed thereover so as to enclose it, in order, at least one
intermediate layer 2 and a cover 3 as the outermost layer. Of these
components, the intermediate layer is made of a resin composition
containing a heated mixture of (a) an olefin-unsaturated carboxylic
acid random copolymer and/or an olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester random copolymer or (d) a
metal ion neutralization product of an olefin-unsaturated
carboxylic acid random copolymer and/or an olefin-unsaturated
carboxylic acid-unsaturated carboxylic acid ester random copolymer
alone, or both components (a) and (d), in combination with (b) a
fatty acid or fatty acid derivative having a molecular weight of at
least 280, and (c) a basic inorganic metal compound capable of
neutralizing the acid groups in the foregoing components.
Components (a) to (d) are described in detail below.
The olefin in the above component (a) has a number of carbons which
is generally at least 2 but not more than 8, and preferably not
more than 6. Specific examples include ethylene, propylene, butene,
pentene, hexene, heptene and octene. Ethylene is especially
preferred.
Examples of the unsaturated carboxylic acid include acrylic acid,
methacrylic acid, maleic acid and fumaric acid. Acrylic acid and
methacrylic acid are especially preferred.
Moreover, the unsaturated carboxylic acid ester is preferably a
lower alkyl ester of the above unsaturated carboxylic acid.
Specific examples include methyl methacrylate, ethyl methacrylate,
propyl methacrylate, butyl methacrylate, methyl acrylate, ethyl
acrylate, propyl acrylate and butyl acrylate. Butyl acrylate
(n-butyl acrylate, i-butyl acrylate) is especially preferred.
The random copolymer of component (a) may be obtained by random
copolymerizing the above components in accordance with a known
method. Here, it is recommended that the unsaturated carboxylic
acid content (acid content) present in the random copolymer be
generally at least 2 wt %, preferably at least 6 wt %, and more
preferably at least 8 wt %, but not more than 25 wt %, preferably
not more than 20 wt %, and even more preferably not more than 15 wt
%. At a low acid content, the material may have a lower resilience,
whereas at a high acid content, the processability of the material
may decrease.
The random copolymer neutralization product serving as component
(d) can be obtained by neutralizing some of the acid groups on the
above-described random copolymer with metal ions. Here,
illustrative examples of the metal ions for neutralizing the acid
groups include Na.sup.+, K.sup.+, Li.sup.+, Zn.sup.++, Cu.sup.++,
Mg.sup.++, Ca.sup.++, Co.sup.++, Ni.sup.++ and Pb.sup.++. Of these,
preferred use can be made of, for example, Na.sup.+, Li.sup.+,
Zn.sup.++ and Mg.sup.++. The use of Zn.sup.++ is even more
preferred. No particular limitation is imposed on the degree to
which such metal ions neutralize the random copolymer. Such a
neutralization product may be obtained by a known method. For
example, a compound such as a formate, acetate, nitrate, carbonate,
bicarbonate, oxide, hydroxide or alkoxide of the above-mentioned
metal ions may be used to introduce the metal ions to the
above-described random copolymer.
Illustrative examples of the random copolymers that may be used as
above component (a) include Nucrel AN4311, Nucrel AN4318 and Nucrel
1560 (all products of DuPont-Mitsui Polychemicals Co., Ltd.).
Illustrative examples of the random copolymer neutralization
products that may be used as above component (d) include Himilan
1554, Himilan 1557, Himilan 1601, Himilan 1605, Himilan 1706,
Himilan 1855, Himilan 1856 and Himilan AM7316 (all products of
DuPont-Mitsui Polychemicals Co., Ltd.), and Surlyn 6320, Surlyn
7930 and Surlyn 8120 (all products of E.I. DuPont de Nemours &
Co.). The use of a zinc-neutralized ionomer resin (e.g., Himilan
AM7316) is especially preferred.
The random copolymer of above component (a) and the neutralization
product of above component (d) may be used, either singly or in
combination, as the base resin. If both are used in combination,
the proportions therebetween are not subject to any particular
limitation.
Above component (b) is a fatty acid or fatty acid derivative having
a molecular weight of at least 280. It is a component which
improves the flow properties of the heated mixture. Compared with
the thermoplastic resin serving as above component (a), this
component has a very low molecular weight and helps to greatly
increase the melt viscosity of the mixture. Because the fatty acid
(or derivative thereof) of the invention has a molecular weight of
at least 280 and includes a high content of acid groups (or
derivatives thereof), the loss in resilience due to the addition
thereof is small.
The fatty acid or fatty acid derivative of component (b) may be an
unsaturated fatty acid (or derivative thereof) containing a double
bond or triple bond on the alkyl moiety, or it may be a saturated
fatty acid (or derivative thereof) in which the bonds on the alkyl
moiety are all single bonds. It is recommended that the number of
carbons on the molecule be generally at least 18, but not more than
80, and preferably not more than 40. Too few carbons may make it
impossible to improve the heat resistance, which is an object of
the invention, and may also make the acid group content so high as
to diminish the flow-improving effect due to interactions with acid
groups present in the base resin. On the other hand, too many
carbons increases the molecular weight, as a result of which the
flow-improving effect may diminish.
Specific examples of the fatty acid of component (b) include
stearic acid, 1,2-hydroxystearic acid, behenic acid, oleic acid,
linoleic acid, linolenic acid, arachidic acid and lignoceric acid.
Of these, stearic acid, arachidic acid, behenic acid and lignoceric
acid are preferred.
The fatty acid derivative in the invention is a compound in which
the proton on the acid group of the fatty acid has been replaced.
Such fatty aid derivatives are exemplified by metallic soaps in
which the proton on the acid group of the fatty acid has been
replaced with a metal ion. Examples of the metal ion include
Li.sup.+, Ca.sup.++, Mg.sup.++, Zn.sup.++, Mn.sup.++, Al.sup.+++,
Ni.sup.++, Fe.sup.++, Fe.sup.+++, Cu.sup.++, Sn.sup.++, Pb.sup.++
and Co.sup.++. Of these, Ca.sup.++, Mg.sup.++ and Zn.sup.++ are
especially preferred.
Specific examples of fatty acid derivatives that may be used as
component (b) include magnesium stearate, calcium stearate, zinc
stearate, magnesium 12-hydroxystearate, calcium 12-hydroxystearate,
zinc 12-hydroxystearate, magnesium arachidate, calcium arachidate,
zinc arachidate, magnesium behenate, calcium behenate, zinc
behenate, magnesium lignocerate, calcium lignocerate and zinc
lignocerate. Of these, magnesium stearate, calcium stearate, zinc
stearate, magnesium arachidate, calcium arachidate, zinc
arachidate, magnesium behenate, calcium behenate, zinc behenate,
magnesium lignocerate, calcium lignocerate and zinc lignocerate are
preferred.
Moreover, use may be made of known metal soap-modified ionomers
(such as those mentioned in U.S. Pat. Nos. 5,312,857, 5,306,760 and
International Application WO 98/46671) when using the
above-described component (a) and/or (d) and component (b).
In the intermediate layer material of the invention, a basic
inorganic filler capable of neutralizing acid groups in above
component (a) and/or (d) and in above component (b) may be added as
component (c). However, as mentioned in the prior-art examples,
when component (a) and/or (d) and component (b) alone, and in
particular a metal-modified ionomer resin alone (e.g., a metal
soap-modified ionomer resin of the type mentioned in the above
patent publications, alone), is heated and mixed, as shown below,
the metallic soap and un-neutralized acid groups present on the
ionomer undergo exchange reactions, generating a fatty acid.
Because the fatty acid has a low thermal stability and readily
vaporizes during molding, it causes molding defects. Moreover, if
the fatty acid thus generated deposits on the surface of the molded
material, it may substantially lower paint film adhesion.
##STR00001## (i) un-neutralized acid group present on the ionomer
resin (ii) metallic soap (iii) fatty acid X: metal cation
To solve this problem, the material includes also, as component
(c), a basic inorganic metal compound which neutralizes the acid
groups present in above components (a) and/or (d) and component
(b). The inclusion of component (c) as an essential ingredient
confers excellent properties. That is, the acid groups in above
components (a) and/or (d) and component (b) are neutralized, and
synergistic effects from the blending of each of these respective
components increase the thermal stability of the heated mixture
while at the same time conferring a good moldability and thus
enhancing the resilience as a golf ball-forming material.
It is recommended that above component (c) be a basic inorganic
metal compound, preferably a monoxide, which is capable of
neutralizing acid groups in above components (a) and/or (d) and in
component (b). Because such compounds have a high reactivity with
the ionomer resin and the reaction by-products contain no organic
matter, the degree of neutralization of the heated mixture can be
increased without a loss of thermal stability.
The metal ions used here in the basic inorganic metal compound are
exemplified by Li.sup.+, Na.sup.+, K.sup.+, Ca.sup.++, Mg.sup.++,
Zn.sup.++, Al.sup.+++, Ni.sup.+, Fe.sup.++, Fe.sup.+++, Cu.sup.++,
Mn.sup.++, Sn.sup.++, Pb.sup.++ and Co.sup.++. Illustrative
examples of the inorganic metal compound include basic inorganic
fillers containing these metal ions, such as magnesium oxide,
magnesium hydroxide, magnesium carbonate, zinc oxide, sodium
hydroxide, sodium carbonate, calcium oxide, calcium hydroxide,
lithium hydroxide and lithium carbonate. As noted above, a monoxide
is preferred. The use of magnesium oxide, which has a high
reactivity with ionomer resins, is especially preferred.
The above intermediate layer material prepared as described above
from components (a), (d), (b) and (c) can be provided with an
improved thermal stability, moldability and resilience. To achieve
these ends, the components must be formulated in certain
proportions. Specifically, it is essential to include, per 100
parts by weight of component (a) and/or component (d) (referred to
below as the "base resin"), at least 5 parts by weight, but not
more than 80 parts by weight, preferably not more than 40 parts by
weight, and more preferably not more than 20 parts by weight, of
component (b); and at least 0.1 part by weight but not more than 20
parts by weight, preferably not more than 10 parts by weight, and
more preferably not more than 5 parts by weight, of component (c).
Too little component (b) lowers the melt viscosity, resulting in a
poor processability, whereas too much lowers the durability. Too
little component (c) fails to improve thermal stability and
resilience, whereas too much instead lowers the heat resistance of
the composition due to the presence of excess basic inorganic metal
compound.
The above-described material may be used directly as the heated
mixture, or other ingredients may be suitably included in the
mixture. In either case, the heated mixture preferably has a melt
flow rate, as measured according to JIS K-7210, of at least 0.5
g/10 min, and more preferably at least 1.0 g/10 min. Because
relatively low flow properties in the intermediate layer material
enables the desired resilience to be achieved, it is desirable for
the heated mixture to also have low flow properties. However, if
the heated mixture has a low melt flow rate, the result will be a
marked decline in processability.
It is preferable for the above mixed material to be characterized
by, in infrared absorption spectroscopy, the relative absorbance at
the absorption peak attributable to carboxylate anion stretching
vibrations at 1530 to 1630 cm.sup.-1 with respect to the absorbance
at the absorption peak attributable to carbonyl stretching
vibrations normally detected at 1690 to 1710 cm.sup.-1. This ratio
may be expressed as follows: (absorbance at absorption peak for
carboxylate anion stretching vibrations)/(absorbance at absorption
peak for carbonyl stretching vibrations).
Here, "carboxylate anion stretching vibrations" refers to
vibrations by carboxyl groups from which the proton has dissociated
(metal ion-neutralized carboxyl groups), and "carbonyl stretching
vibrations" refers to vibrations by undissociated carboxyl groups.
The ratio between these respective peak intensities depends on the
degree of neutralization. In the ionomer resins having a degree of
neutralization of about 50 mol % which are commonly used, the ratio
between these peak absorbances is about 1:1.
To improve the thermal stability, moldability and resilience of the
intermediate layer material, it is recommended that the above
heated mixture have a carboxylate anion stretching vibration peak
absorbance which is at least 1.5 times, and preferably at least 2
times, the carbonyl stretching vibration peak absorbance. The
absence of any carbonyl stretching vibration peak is especially
preferred.
The thermal stability of the above heated mixture can be measured
by thermogravimetry. It is recommended that, in thermogravimetry,
the heated mixture have a weight loss at 250.degree. C., based on
the weight of the mixture at 25.degree. C., of generally not more
than 2 wt %, preferably not more than 1.5 wt %, and more preferably
not more than 1 wt %.
Although not subject to any particular limitation, it is
recommended that the specific gravity of the heated mixture proper
be generally at least 0.9, but not more than 1.5, preferably not
more than 1.3, and more preferably not more than 1.1.
The heated mixed is obtained by heating and mixing the
above-described component (a) and/or component (d), component (b)
and component (c), and has an optimized melt flow rate.
It is recommended that at least 90 mol %, and most preferably at
least 100 mol %, of the acid groups in the heated mixture be
neutralized. Such a high degree of neutralization makes it possible
to more reliably suppress the exchange reactions that are a problem
when only the above-described base resin and the fatty acid (or a
derivative thereof) are used, thus preventing the formation of
fatty acids. As a result, there can be obtained a material which
has a greatly increased thermal stability and a good moldability,
and which moreover has a much improved resilience compared with
prior-art ionomer resins.
Here, with regard to the neutralization of the above heated
mixture, to more reliably achieve both a high degree of neutrality
and good flow, it is recommended that the acid groups in the heated
mixture be neutralized with transition metal ions and with alkali
metal and/or alkaline earth metal ions. Transition metal ions have
a weaker ionic cohesion than alkali metal and alkaline earth metal
ions and so neutralize some of the acid groups in the heated
mixture, enabling the flow properties to be significantly
improved.
The molar ratio between the transition metal ions and the alkali
metal and/or alkaline earth metal ions is set as appropriate,
generally in a range of 10:90 to 90:10, and preferably 20:80 to
80:20. Too low a molar ratio of transition metal ions may fail to
provide sufficient improvement in the flow properties of the
material. On the other hand, a molar ratio that is too high may
lower the resilience.
Specific examples of such metal ions include zinc ions as the
transition metal ions and at least one type of ion selected from
among sodium, lithium and magnesium ions as the alkali metal or
alkaline earth metal ions.
No particular limitation is imposed on the method used to obtain
the heated mixture in which the acid groups have been neutralized
with transition metal ions and alkali metal or alkaline earth metal
ions. Specific examples of methods of neutralization with
transition metal ions, particularly zinc ions, include a method in
which a zinc soap is used as the fatty acid derivative, a method in
which a zinc ion neutralization product is included as component
(d) in the base resin (e.g., a zinc-neutralized ionomer resin), and
a method in which zinc oxide is used as the basic inorganic metal
compound of component (c).
To obtain the intermediate layer material, it suffices to use the
above heated mixture as an essential component. The advantageous
effects of the invention can be effectively exhibited by including
the heated mixture in an amount, expressed as a proportion of the
overall intermediate layer material (overall resin composition), of
preferably at least 50 wt %, more preferably at least 60 wt %, and
even more preferably at least 70 wt %. In addition, various
additives such as pigments, dispersants, antioxidants, ultraviolet
absorbers and optical stabilizers may be included within the
foregoing resin composition in which the above heated mixture
serves as an essential component. To improve the feel of the golf
ball on impact, the material of the invention may also include, in
addition to the above essential components, various non-ionomeric
thermoplastic elastomers. Illustrative examples of such
non-ionomeric thermoplastic elastomers include olefin elastomers,
styrene elastomers, ester elastomers and urethane elastomers. The
use of olefin elastomers and styrene elastomers is especially
preferred. A commercial product such as Dynaron, a hydrogenated
polymer produced by JSR Corporation, may be used as the olefin
elastomer.
The method of preparing the above-described resin composition is
not subject to any particular limitation. For example, mixture may
be carried out under heating at a temperature of between 150 and
250.degree. C. in an internal mixer such as a kneading-type
twin-screw extruder, a Banbury mixer or a kneader. The method of
incorporating the various additives other than the essential
ingredients in the above resin composition, while not subject to
any particular limitation, is exemplified by a method in which the
additives are blended together with the essential ingredients and
at the same time mixed under heating, and a method in which the
essential ingredients are first mixed together under heating,
following which the optional additives are added and further mixing
under heating is carried out.
The method of forming the intermediate layer is not subject to any
particular limitation. For example, the intermediate layer may be
formed by a known injection molding or compression molding process
using the above resin composition. When injection molding is
employed, the process may involve placing a prefabricated core at a
given position in an injection molding mold, then introducing the
above-described material into the mold. When compression molding is
employed, the process may involve producing a pair of half cups
from the above-described material, enclosing the core with these
cups, then applying heat and pressure within a mold. If molding
under heat and pressure is carried out, the molding conditions
employed may be a temperature of from 120 to 170.degree. C. and a
period of from 1 to 5 minutes.
The intermediate layer is formed of a resin composition composed
primarily of the above-described heated mixture, but is not limited
to a single layer. If the intermediate layer is composed of two or
more layers, at least one such layer will be made of the above
heated mixture. Any of various known resin materials may be used in
the other layer or layers.
Specifically, use may be made of, for example, the rubber
composition described above as the core-forming material, or a
thermoplastic resin.
Thermoplastic resins that may be used as the other intermediate
layer material are exemplified by ionomer resins and by
thermoplastic elastomers such as polyester elastomers, polyamide
elastomers, polyurethane elastomers, olefin elastomers and styrene
elastomers. Such elastomers are commercially available as, for
example, Hytrel (produced by DuPont-Toray Co., Ltd.), Pelprene
(produced by Toyobo Co., Ltd.), Pebax (produced by Atochem Co.),
Pandex (Dainippon Ink & Chemicals, Inc.), Santoprene (Monsanto)
and Tuftec (Asahi Chemical Industry Co., Ltd.). Commercially
available ionomer resins include Himilan (produced by DuPont-Mitsui
Polychemicals Co., Ltd.), Surlyn (E.I. DuPont de Nemours &
Co.), and Iotek (Exxon Corporation).
Various additives such as inorganic fillers may be included in
suitable amounts within the thermoplastic resin. Illustrative
examples of suitable inorganic fillers include barium sulfate and
titanium dioxide. These inorganic fillers may be surface treated to
facilitate dispersion in the material.
In those cases where another material is used, the intermediate
layer may likewise be formed by a known process. The process
employed in such cases may be similar to the above-described
intermediate layer-forming process in which the heated mixture is
used.
Here, the intermediate layer is formed to a thickness of at least
0.6 mm, and preferably at least 0.9 mm, but not more than 1.6 mm,
and preferably not more than 1.4 mm. If the intermediate layer is
thinner than the above range, the durability to cracking will
worsen and the high resilience effect of the material will
decrease. Conversely, if the intermediate layer is thicker than the
above range, the spin rate will increase excessively and the feel
on impact will be harder.
The Shore D hardness of the intermediate layer is set to at least
45 but not more than 55. If the intermediate layer is softer than
the above range, the spin rate will increase, the distance traveled
by the ball will decrease, and the ball will have a smaller
rebound. On the other hand, if the intermediate layer is harder
than the above range, the ball will have a harder feel on
impact.
The cover (outermost layer) of the inventive golf ball may be
formed primarily of a thermoplastic resin or a thermoplastic
elastomer. Examples include thermoplastic resins such as ionomer
resins, and various types of thermoplastic elastomers. For example,
use may be made of a polyester-type thermoplastic elastomer, a
polyamide-type thermoplastic elastomer, a polyurethane-type
thermoplastic elastomer, an olefin-type thermoplastic elastomer or
a styrene-type thermoplastic elastomer. The use of an ionomer resin
or a polyurethane-type thermoplastic elastomer is preferred.
Examples of commercial ionomer resins, etc. that may be used
include Himilan (produced by DuPont-Mitsui Polychemicals Co.,
Ltd.), Surlyn (E.I. DuPont de Nemours & Co.), Iotek (Exxon
Corporation) and T-8190 (Dainippon Ink & Chemicals, Inc.).
Suitable amounts of various additives such as inorganic fillers may
be included in the cover material. Preferred inorganic fillers
include those which may be used in the above-described intermediate
layer.
As with the intermediate layer, the cover may be formed of the
above-described material by an injection molding process or a
compression molding process.
The cover material is typically set to a higher melt flow rate than
the intermediate layer material, the difference between the two
preferably being at least 1.0 g/10 min. As noted subsequently, the
cover is formed to a thickness of not more than 1.6 mm. In the
absence of a sufficient degree of flow, cover formation will be
poor, which may result in a poor cover quality.
The cover has a thickness of at least 0.6 mm, and preferably at
least 0.8, but not more than 1.6 m, and preferably not more than
1.4 mm. If the cover is thinner than the above range, the
durability to cracking and the scuff resistance will worsen.
Moreover, if the cover is thinner than the above range, the cover
rigidity will decrease and the intermediate layer will be flattened
to such a degree as to diminish the high resilience effect of the
intermediate layer material. On the other hand, if the cover layer
is thicker than the above range, the feel of the ball will
harden.
In the practice of the invention, it is essential for the
intermediate layer and the cover to have a combined thickness of at
least 1.8 mm, but not more than 2.8 mm. If the thickness of the
intermediate layer and the cover combined is smaller than the above
range, the ball will have a poor durability to cracking and a poor
scuff resistance. Moreover, the high resilience effect of the
intermediate layer will decrease and the cover rigidity will
decrease, preventing a reduction in the spin rate. On the other
hand, if the combined thickness of these two layers is greater than
the above range, the ball will have a harder feel on impact, in
addition to which the spin rate will increase, lowering the
distance traveled by the ball.
In addition, it is essential for the cover to have a Shore D
hardness of at least 63 but not more than 66. If the Shore D
hardness is softer than this range, the spin rate will rise and the
distance traveled by the ball will decrease. In addition, the
rebound by the ball will decrease. Moreover, in such a case, the
rigidity of the cover will decrease, resulting in excessive
flattening of the intermediate layer, thus lowering the high
resilience effect of the intermediate layer material. Conversely,
if the Shore D hardness of the cover is higher than the above
range, the ball will have a harder feel on impact.
No particular limitation is imposed on the deflection (mm) of the
inventive golf ball when subjected to a final compressive load of
130 kgf from an initial load state of 10 kgf. However, to
successfully manifest the advantageous effects of the invention,
the deflection of the ball is preferably at least 2.6 mm, and more
preferably at least 2.8 mm, but preferably not more than 3.5 mm,
and more preferably not more than 3.3 mm. If the ball deflection is
lower than the above range, the feel on impact may harden, which is
undesirable. On the other hand, if the ball deflection is higher
than the above range, the overall ball may undergo excessive
deformation, reducing the advantageous effects of the intermediate
layer.
As shown in FIG. 1, numerous dimples are formed on the surface of
the inventive ball by a conventional method. To enhance the
aerodynamic performance of the ball, these dimples D preferably
having a surface coverage of at least 79%. The number of dimples D,
although not subject to any particular limitation, is preferably
set within a range of from 250 to 370, and most preferably from 270
to 350. As used herein, the "overall volume" of the dimples D on
the surface of a ball, although not shown in the diagram, signifies
the volume of the region enclosed by the wall of a dimple D and the
curved surface defined by the land areas at the surface of the
ball, summed for all the dimples on the ball. This overall volume
is set to preferably from 400 to 700 mm.sup.3, and especially from
450 to 650 mm.sup.3. If the number, surface coverage and overall
volume of these dimples are smaller than the above ranges, the lift
of the ball may increase, shortening the distance of travel. On the
other hand, if these parameters are higher than the above ranges,
the lift of the ball may decrease, shortening the distance of
travel.
In the practice of the invention, the shape of the dimples D,
although not specifically shown in the diagrams, is not limited to
the commonly used circular shape as seen from above. That is, it is
also possible to use various distinctive dimple shapes, such as
polygonal shapes (e.g., triangular, quadrangular, pentagonal and
hexagonal shapes), dewdrop shapes and oval shapes, either alone or
in suitable combinations thereof.
Moreover, in the present invention, because the ball is, as noted
above, designed so as to have a low-spin construction, it is
important to carry out a dimple design that has the effect of
helping to preserve lift even in low-spin regions of the ball's
trajectory after it has been struck.
The golf ball of the invention may be manufactured so as to conform
with the Rules of Golf for competitive play. That is, it may be
formed to a ball diameter which is not less than 42.67 mm and a
weight which is not more than 45.93 g.
As explained above, in the golf ball of the present invention, by
increasing the hardnesses of the cover and intermediate layer
enclosing the core up to a limit that does not compromise the feel
of the ball, and by also forming the intermediate layer of a
specific resin mixture that is a high-resilience material, the
timing of the force which suppresses the spin of the ball after it
has been hit with a driver is speeded up, making it possible to
achieve a reduction in the spin rate and significantly increase the
distance traveled by the ball. Moreover, the ball has a good feel
on impact and a high durability to cracking.
EXAMPLES
Examples of the invention and Comparative Examples are given below
by way of illustration, and not by way of limitation.
Examples 1 to 4, Comparative Examples 1 to 9
Cores were produced by vulcanizing rubber compositions formulated
as shown in Table 1 (ingredient amounts are indicated in parts by
weight) at 155.degree. C. for 15 minutes. In each example, the
intermediate layer material of the formulation shown in Table 2 and
the cover material shown in Table 3 were successively
injection-molded over the core, thereby producing a three-piece
solid golf ball having an intermediate layer and a cover formed
about the core. The physical properties and evaluation results for
the respective golf balls are presented in Table 4 (examples
according to the invention) and Table 5 (comparative examples).
TABLE-US-00001 TABLE 1 (parts by weight) A B C D E F G
Polybutadiene 100 100 100 100 100 100 100 Polyisoprene 0 0 0 0 0 0
0 Zinc acrylate 24.2 22.9 22.9 24.2 21.4 25.2 27.2 Peroxide (1) 0.6
0.6 0.6 0.6 0.6 0.6 0 Peroxide (2) 0.6 0.6 0.6 0.6 0.6 0.6 3 Sulfur
0 0 0 0 0 0 0.1 Antioxidant 0.1 0.1 0.1 0.1 0.1 0.1 0 Zinc oxide
29.4 29.9 38.7 26.6 30.5 29.0 27.4 Zinc salt of 0 0 0 0 0 0 0
pentachlorothiophenol
Trade names of the primary materials appearing in Table 1 are as
follows. Polybutadiene: Produced by JSR Corporation under the trade
name "BR730." Polyisoprene: Produced by JSR Corporation under the
trade name "IR2200." Peroxide (1): Dicumyl peroxide, produced by
NOF Corporation under the trade name "Percumyl D." Peroxide (2): A
mixture of 1,1-di(t-butylperoxy)cyclohexane and silica, produced by
NOF Corporation under the trade name "Perhexa C-40." Sulfur: Zinc
white-sulfur mixture, produced by Tsurumi Chemical Industry Co.,
Ltd. Antioxidant: Produced by Ouchi Shinko Chemical Industry Co.,
Ltd. under the trade name "Nocrac NS-6."
TABLE-US-00002 TABLE 2 a b c d Ionomer AM7318 65 S8150 S8120 75 75
S8320 75 TPO Dynaron 6100P 25 25 35 25 Fatty acid Behenic acid 20
20 20 20 Cation source Ca(OH).sub.2 4 4 4 2.9 MFR (g/10 min) 0.9
0.9 0.9 2.1 Notes: 1) Formulated amounts are given in parts by
weight. 2) The MFR (g/10 min) is the value obtained by measurement
at a test temperature of 190.degree. C. and a test load of 21.18 N
(2.16 kgf) in accordance with JIS-K 7210.
Trade names of the primary materials appearing in Table 2 are as
follows. AM7318: An ionomer resin which is an ethylene-methacrylic
acid copolymer neutralized with sodium ions. Available from
DuPont-Mitsui Polychemicals Co., Ltd. Surlyn 8150: An ionomer resin
which is an ethylene-methacrylic acid copolymer neutralized with
sodium ions. Available from E.I. DuPont de Nemours & Co. Surlyn
8120: An ionomer resin which is an ethylene-methacrylic
acid-acrylic acid ester copolymer neutralized with sodium ions.
Available from E.I. DuPont de Nemours & Co. Surlyn 8320: An
ionomer resin which is an ethylene-methacrylic acid-acrylic acid
ester copolymer neutralized with sodium ions. Available from E.I.
DuPont de Nemours & Co. Dynaron 6100P: A hydrogenated polymer
(olefin-based thermoplastic elastomer) available from JSR
Corporation. Behenic acid: NAA-222S (trade name), available from
NOF Corporation as a powder. Calcium hydroxide: CLS-B, produced by
Shiraishi Kogyo Kaisha, Ltd.
TABLE-US-00003 TABLE 3 e f Ionomer H1605 40 H1706 50 H1601 50 10
H1557 50 Fatty acid Behenic acid 0 0 Cation source Ca(OH).sub.2 0 0
Additives TiO.sub.2 3 3 Blue 0.04 0.04 MFR (g/10 min) 2.3 2.5 Note:
Formulated amounts are given in parts by weight.
Trade names of the primary materials appearing in Table 3 are as
follows. Himilan 1605: An ionomer resin which is an
ethylene-methacrylic acid copolymer neutralized with sodium ions.
Available from DuPont-Mitsui Polychemicals Co., Ltd. Himilan 1706:
An ionomer resin which is an ethylene-methacrylic acid copolymer
neutralized with zinc ions. Available from DuPont-Mitsui
Polychemicals Co., Ltd. Himilan 1601: An ionomer resin which is an
ethylene-methacrylic acid copolymer neutralized with sodium ions.
Available from DuPont-Mitsui Polychemicals Co., Ltd. Himilan 1557:
An ionomer resin which is an ethylene-methacrylic acid copolymer
neutralized with zinc ions. Available from DuPont-Mitsui
Polychemicals Co., Ltd. Titanium oxide: Tipaque R550 (trade name),
available from Ishihara Sangyo Kaisha, Ltd. Blue (blue pigment):
Ultramarine Blue EP-62 (trade name), available from Holliday
Pigments.
TABLE-US-00004 TABLE 4 Example 1 2 3 4 Core Diameter (mm) 37.3 37.3
37.7 37.7 Formulation A B A B Deflection (mm) 3.6 4.1 3.6 4.1
Initial velocity (m/s) 76.8 76.8 76.8 76.8 Center hardness (Shore
D) 28 26 28 28 Surface hardness (Shore D) 40 38 40 40 Surface -
Center (Shore D) 12 12 12 12 Intermediate Diameter (mm) 40.0 40.0
40.2 40.2 layer Thickness (mm) 1.35 1.35 1.25 1.25 Hardness (Shore
D) 51 51 51 51 Formulation b b b b Cover Thickness (mm) 1.35 1.35
1.25 1.25 Hardness (Shore D) 63 63 63 63 Formulation f f f f Ball
Diameter (mm) 42.7 42.7 42.7 42.7 Weight (g) 45.4 45.4 45.4 45.4
Deflection (mm) 2.8 3.2 2.9 3.3 Initial velocity (m/s) 77.3 77.3
77.3 77.3 Thickness of intermediate layer + cover (mm) 2.7 2.7 2.5
2.5 Flight Spin rate (rpm) 2510 2480 2500 2460 performance Initial
velocity (m/s) 62.6 62.2 62.7 62.3 #1 (driver) Distance (m) 232.0
231.2 233.1 231.5 HS 45 Feel on impact (driver) soft soft soft soft
Durability to cracking good good good good Intermediate layer MFR
(g/10 min) 0.9 0.9 0.9 0.9 Cover MFR (g/10 min) 2.5 2.5 2.5 2.5
(Cover - Intermediate layer) MFR (g/10 min) 1.6 1.6 1.6 1.6
TABLE-US-00005 TABLE 5 Comparative Example 1 2 3 4 5 6 7 8 9 Core
Diameter (mm) 37.3 35.7 39.5 37.3 37.3 37.3 37.3 37.3 37.3
Formulation G C D B B B E F B Deflection (mm) 4.2 4.1 3.6 4.1 4.1
4.1 4.6 3.3 4.1 Initial velocity (m/s) 76.8 76.8 76.8 76.8 76.8
76.8 76.8 76.8 77.0 Center hardness (Shore D) 26 26 28 28 26 26 24
26 26 Surface hardness (Shore D) 48 37 41 40 38 38 36 38 38 Surface
- Center (Shore D) 22 11 13 12 12 12 12 12 12 Intermediate Diameter
(mm) 40 39.2 41.1 40 40 40 40 40 40 layer Thickness (mm) 1.35 1.75
0.8 1.35 1.35 1.35 1.35 1.35 1.35 Hardness (Shore D) 51 51 51 42 58
51 51 51 51 Formulation b b b a c b b b d Cover Thickness (mm) 1.35
1.75 0.8 1.35 1.35 1.35 1.35 1.35 1.35 Hardness (Shore D) 63 63 63
63 63 60 63 63 63 Formulation f f f f f e f f f Ball Diameter (mm)
42.7 42.7 42.7 42.7 42.7 42.7 42.7 42.7 42.7 Weight (g) 45.4 45.6
45.3 45.4 45.4 45.4 45.4 45.4 45.4 Deflection (mm) 3.2 3.0 3.0 3.3
3.1 3.3 3.6 2.5 3.2 Initial velocity (m/s) 77.3 77.5 77.3 77.2 77.4
77.2 77.3 77.3 77.3 Thickness of intermediate layer + 2.7 3.5 1.6
2.7 2.7 2.7 2.7 2.7 2.7 cover (mm) Flight Spin rate (rpm) 2620 2650
2630 2610 2450 2660 2450 2710 2580 performance Initial velocity
(m/s) 62.3 62.7 62.5 62.3 62.4 62.0 61.2 63.1 62.2 #1 (driver)
Distance (m) 228.5 227.8 228.2 228.6 232.5 227.2 228.6 229.1 229.4
HS 45 Feel on impact (driver) soft hard soft soft hard soft soft
hard soft Durability to cracking good good NG good fair good NG
good good Intermediate layer MFR (g/10 min) 0.9 0.9 0.9 0.9 0.9 0.9
0.9 0.9 2.1 Cover MFR (g/10 min) 2.5 2.5 2.5 2.5 2.5 2.3 2.5 2.5
2.5 (Cover - Intermediate layer) MFR 1.6 1.6 1.6 1.6 1.6 1.4 1.6
1.6 0.4 (g/10 min)
Details concerning tests and evaluations conducted on the physical
properties, flight performance, feel on impact, and durability to
cracking of the golf balls obtained in the examples of the
invention and the comparative examples are given below.
Deflection of Core and Ball
The deformation (mm) of a core or golf ball when subjected to a
final compressive load of 130 kgf from an initial load state of 10
kgf.
Core Center Hardness, Core Surface Hardness
These are Shore D hardnesses; that is, hardnesses as measured with
an ASTM D2240 type D durometer. The core surface hardness was
measured at the surface of the core. The core center hardness was
measured at the center of a core that had been cut in half.
Intermediate Layer Hardness, Cover Hardness
These are Shore D hardnesses; that is, hardnesses as measured with
an ASTM D2240 type D Durometer, based on JIS K-6253. Each of these
hardnesses refers not to the surface hardness of the sphere covered
by the intermediate layer or the cover, but rather to the measured
surface hardness of a resin sheet.
Flight Performance
The distance traveled by the ball when hit at a head speed (HS) of
45 m/s with a driver (TourStage X-Drive Type 405, manufactured by
Bridgestone Sports Co., Ltd.; loft angle, 9.5.degree.) mounted on a
swing robot (Miyamae Co., Ltd.) was measured. The initial velocity
and spin rate were measured from high-speed camera images of the
ball taken immediately after impact.
Feel on Impact
Each ball was hit by five skilled amateur golfers having handicaps
of less than 10, and assigned a score of 1 to 5 according to the
following criteria.
5: Very soft
4: Soft
3: Ordinary
2: Hard
1: Very hard
The scores obtained for each ball were then averaged, based on
which the feel of the ball was assigned one of the three ratings
indicated below.
Soft: Average score for the five golfers was above 4 Ordinary:
Average score for the five golfers was from 2 to 4 Hard: Average
score for the five golfers was below 2 Durability to Cracking
The number of shots that had been taken with the ball in Example 2
when its initial velocity fell below 97% of the average initial
velocity for the first 10 shots was assigned a durability index of
"100," based upon which durability indices for the balls in the
other examples were determined. The durabilities of the balls in
the respective examples were rated according to the following
criteria. The average value for N=3 balls was used as the basis for
evaluation in each example. Good: Durability index was 110 or more
Fair: Durability index was at least 90 but less than 110 NG:
Durability index was less than 90
As is apparent from the results in Table 5, because the golf balls
obtained in the comparative examples had the ball constructions
indicated below, they were inferior to the golf balls of the
present invention (Table 4) in at least one of the ball
characteristics assessed. The details are given below.
In Comparative Example 1, the core had a large hardness
distribution, resulting in a high spin rate on shots with a driver
(number 1 wood).
In Comparative Example 2, the large combined thickness of the
intermediate layer and the cover resulted in a high spin rate and a
poor distance. Moreover, the ball had a hard feel on impact.
In Comparative Example 3, the small combined thickness of the
intermediate layer and the cover resulted in a high spin rate and a
poor distance. Moreover, the ball had a poor durability to
cracking.
In Comparative Example 4, the intermediate layer was too soft,
resulting in a high spin rate and a poor distance.
In Comparative Example 5, the intermediate layer was too hard,
resulting in a hard feel on shots with a driver (number 1 wood).
Moreover, the durability to cracking was poor.
In Comparative Example 6, the cover was too soft, resulting in a
high spin rate and a poor distance.
In Comparative Example 7, the finished ball was too soft, lowering
the initial velocity. As a result, the ball had a poor distance.
Moreover, the durability to cracking was poor.
In Comparative Example 8, the finished ball was too hard, as a
result of which the ball had a high spin rate and a poor distance.
Moreover the ball had a hard feel on impact.
In Comparative Example 9, because the intermediate layer had a low
degree of neutralization, the ball had a low rebound, slowing down
the timing of the force that acts to suppress the spin rate. As a
result, the ball ended up having a high spin rate and thus a short
distance.
In Examples of the golf ball, the added amount of
pentachlorothiophenol is 0 part by weight in the composition of the
core and the degree of neutralization of the cover is set
comparatively lower. That is, both of the core and the cover are
made to lower rebound or low resilience, and the degree of
neutralization of the intermediate layer is further enhanced to
improve its resilience, so that a ball construction is created so
as to bring about a spin rate-lowering effect of a highly resilient
intermediate layer.
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